Silurian strontium isotope stratigraphy

Azmy, Karem and Veizer, Ján and Wenzel, Bernd and Bassett, Michael G. and Copper, Paul (1999) Silurian strontium isotope stratigraphy. Geological Society of America Bulletin, 111 (4). pp. 475-483. ISSN 1943-2674

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Abstract

A sample set of 164 calcitic brachiopod shells, covering the entire Silurian Period (∼ 30 m.y.) with a resolution of about 0.7 m.y., was collected from stratotype sections at Anticosti Island (Canada), Wales (United Kingdom), Gotland (Sweden), Podolia (Ukraine), Latvia, and Lithuania. They show 87Sr/86Sr values ranging from 0.707930 to 0.708792 that progressively increase with time. This may indicate an increasing riverine flux of radiogenic Sr into the ocean from weathering of continental sialic rocks due to progressive warming of the climate. Exceptionally high increases in 87Sr/86Sr values were observed in early Llandovery (Rhuddanian), late Llandovery (Telychian), and late Ludlow (Gorstian-Ludfordian boundary) samples. Partial linear regressions, based on a stepwise climbing pattern, with local drops around the Llandovery-Wenlock boundary and in latest Ludlow time, were used to estimate relative ages with a resolution of about ±2 biozones (∼1.5–2 m.y.). The Sr-isotope curve shows distinct inflection points in earliest Wenlock and mid-Prídolí time. These may be used to correlate the Llandovery-Wenlock boundary in the United Kingdom, Gotland, and Lithuania, and the Kaugatuma-Ohesaare boundary in the Baltic states and Podolia.

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